1. Field of the Invention
The invention relates to systems and methods of indirectly measuring the current in hybrid power over ethernet (PoE) architectures without the use of an external series resistor.
2. Related Art
Power over Ethernet (PoE) has become a popular method of delivering power to devices distributed over a network. Compared to the traditional AC power distribution networks, PoE allows for increased efficiency, the ability to provide DC power to devices that require DC power directly and without the need to convert from AC, and the elimination of the need for separate power and data plugs. PoE systems, in general, are well known and are described, for instance, in the IEEE 802.3f and 802.3at specifications, which is incorporated herein by reference in its entirety.
In most PoE systems, power sourcing equipment (PSE) delivers power to one or more powered devices (PDs) over ethernet cabling. Various common PDs include VoIP devices, wireless LAN access ports, Bluetooth access points, network cameras, computing devices, etc. PSEs provide power to the various PDs by turning on transistors (commonly field effect transistors) to allow current to flow to the PD load. It is not uncommon for PSEs to include an integrated circuit component that has an internal transistor to provide current to the load as well as an external transistor that also provides power.
For various reasons, it is frequently desirable to monitor and periodically measure the current flowing through the PSE. For instance, monitoring the current allows the system to detect fluctuations in power usage and adjust to them. In PSEs that employ an external power transistor, this has historically been done by placing a resistive element in series with the external transistor and measuring the voltage drop across the resistor. However, measuring the current this way is inefficient, requires additional components, and results in greater power dissipation.
Thus, there exists a need in the art for systems and methods of measuring the total current in a PSE system that do not require a resistor in series with the external transistor.